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49 votes
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Consider the following three statements about link state and distance vector routing protocols, for a large network with $500$ network nodes and $4000$ links. 

[S1]: The computational overhead in link state protocols is higher than in distance vector protocols. 

[S2]: A distance vector protocol (with split horizon) avoids persistent routing loops, but not a link state protocol. 

[S3]: After a topology change, a link state protocol will converge faster than a distance vector protocol. 

Which one of the following is correct about $S1$, $S2$, and $S3$?

  1. $S1$, $S2$, and $S3$ are all true.
  2. $S1$, $S2$, and $S3$ are all false. 
  3. $S1$ and $S2$ are true, but $S3$ is false.
  4. $S1$ and $S3$ are true, but $S2$ is false.
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5 Answers

Best answer
65 votes
65 votes

The computational overhead in link state protocols is higher than in distance vector protocols because LSR is based upon global knowledge whereas DVR is based upon local knowledge.
Persistent looping can be avoided with the help of split horizon in DVR. There is no concept of persistent looping in LSR, in LSR only temporary loop exists and can automatically be solved by system or router. S2 is false.

And, after a topology change, a link state protocol will converge faster than a distance vector protocol. S3 is true.

Answer is option D.

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22 votes
22 votes
S1 : because of flooding at each router computational overhead in link state routing  is more.
S2 : Persistent loop i.e. count to infinity problem takes place in Distance vector routing not in link state routing.
S3 : Link state routing protocol converges faster when topology changes.
12 votes
12 votes

Link-state: Every node collects complete graph structure Each computes shortest paths from it Each generates own routing table Distance-vector No one has copy of graph Nodes construct their own tables iteratively Each sends information about its table to neighbors

[S1] The computational overhead in link state protocols 
     is higher than in distance vector protocols.
[S2] A distance vector protocol (with split horizon) 
     avoids persistent routing loops, but not a link
     state protocol.
[S3] After a topology change, a link state protocol 
     will converge faster than a distance vector
     protocol.

S1 is clearly true as in Link State all nodes compute shortest path for whole network graph.

S3 is also true as Distance Vector protocol has count to infinity problem and converges slower.

S2 is false. In distance vector protocol, split horizon with poison reverse reduces the chance of forming loops and uses a maximum number of hops to counter the ‘count-to-infinity’ problem. These measures avoid the formation of routing loops in some, but not all, cases

 

http://tinyurl.com/hrolv6l

 

 

4 votes
4 votes

Link-state:
Every node collects complete graph structure
Each computes shortest paths from it
Each generates own routing table

Distance-vector
No one has copy of graph
Nodes construct their own tables iteratively
Each sends information about its table to neighbors 

Source: http://www.cs.cmu.edu/~srini/15-441/S05/lectures/10-Routing.ppt

[S1] The computational overhead in link state protocols
     is higher than in distance vector protocols.
[S2] A distance vector protocol (with split horizon)
     avoids persistent routing loops, but not a link
     state protocol.
[S3] After a topology change, a link state protocol
     will converge faster than a distance vector
     protocol.

S1 is clearly true as in Link State all nodes compute shortest path for whole network graph.S3 is also true as Distance Vector protocol has count to infinity problem and converges slower. S2 is false. In distance vector protocol, split horizon with poison reverse reduces the chance of forming loops and uses a maximum number of hops to counter the 'count-to-infinity' problem. These measures avoid the formation of routing loops in some, but not all, cases

Answer:

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